In general, a hybrid electronic vehicle (hereinafter referred to “HEV”) is configured to use, as a power source, an internal combustion engine and an electric motor. HEVs can be categorized into parallel, serial and mild types in terms of power transfer structure. The HEV uses, as a transmission system, a Dual Clutch Transmission (DCT), wherein an even number gear input shaft and an odd number gear input shaft are used in conjunction with two clutches.
In particular, the HEV in general is operated in either the EV mode (Electric Vehicle Mode) wherein only the motor is used as a power source, and the HEV mode (Hybrid electric Vehicle Mode) wherein the engine and the motor are used together as a power source. An engine clutch system is employed to connect or disconnect the engine and the motor when changing the operation mode between the EV mode and the HEV mode.
For example, the engine clutch system may be formed of a NC (Normally Close) type engine clutch and a motored hydraulic actuator. If the motored hydraulic actuator does not operate, the engine clutch will maintain a connection between the engine and the motor, whereby the power connection between the engine and the motor can be maintained. If the motored hydraulic actuator operates, the engine clutch will disconnect the connection between the engine and the motor, thus disconnecting the power connection between the engine and the motor.
In this way, the HEV can be selectively operated in the EV mode or the HEV mode depending on the operation state of the engine clutch system.
The engine clutch system, however, may be configured to form a flow passage by connecting the motored hydraulic actuator and the engine clutch via a hydraulic line, whereby it may be impossible to control the engine clutch based on the motored hydraulic actuator if oil leaks. Repeated oil leakage may result in a failure in the normal operation of the engine clutch based on the motored hydraulic actuator.